Method for stress wave drilling

ABSTRACT

A method and apparatus for drilling a hole in rock. An openended, hardened, drilling head containing a means for creating high-intensity stress waves capable of spalling rock is utilized to drill the hole. A fluid is passed through the drilling head which removes the spalled rock from the drilling head.

I United States Patent 1 l 3,881,559

Allgood et al. May 6, 1975 [54] METHOD FOR STRESS WAVE DRILLING 3,500,942 3/1970 Smith 175/16 Inventors: J y R. g camaflno; Robe" J. 3,679,007 7/1972 OHare 175/16 Odello, Calabasas, both of Calif. OTHER PUBLlCATlONS 73 Assignee; The United suites f America as What the Russians Have New in Drilling," in The Oil represented by he s f the & Gas Journal, Sept. 14, 1959, Vol. 57, N0. 38, p. Navy, Washington, DC. Maurer, W. C.; Thermal-Spelling, Chemical Drills;" [22] 1974 The oil & Gas Journal, Mar. 4, 1968; pp. 69-73. [21] Appl. NO-I 8 ,3 I Sarapuu, E.; Electra-Energetic Rock Breaking Sys- Rehted Us. Applicafion Dam 212mg; Mining Congress Journal, June 1973, pp. [62] Division of Sn. No. 402,547, Oct. 1, 1973, Pat. No.

Primary Examiner-David H. Brown Attorne A em or Firm-Richard S. Sciascia' Joseph 521 0.8. CI 175/67; 175/15 8 g 7 511 Im. Cl E2lb 7/00 Amand, [58] Field of Search 175/67, 65, 15-17 1 [57] ABSTRACT [56] Referemes Cited A method and apparatus for drilling a hole in rock. An UNITED STATES PATENTS open-ended, hardened, drilling head containing a 2,548,463 4 1951 Blood 175 15 x means for Creating high-intensity Stress Waves capable 2,742,555 4/1956 Murray... of spalling rock is utilized to drill the hole. A fluid is 2,866,622 12/1958 Murray passed through the drilling head which removes the 5,953,353 9/1920 Allen spalled rock from the drilling head.

36,645 5/19 2 Rowley 3,045,766 7/1902 Fleming .1 175/15 x 1 Claim, 4 Drawing Figures i N v 34 36 mils N :7: 1 5:1: /-28 M vim \N iii! 1: Ni /IO {:N M1! 93:1 1 hi at} l I I4 FEET! (EU MAY 8 I975 r 8 2 0 4 3M 0 2 0 3 2 %& w 3 3 m 2 4 I 0. m w r! F METHOD FOR STRESS WAVE DRILLING This is a division of application Ser. No. 402,547 filed Oct. 1, 1973, now US. Pat. No. 3,840,078.

BACKGROUND OF THE INVENTION l. Field of the invention.

This invention relates, generally, to drilling a hole in rock and, more specifically, to utilizing high intensity stress waves to drill a hole in rock.

2. Description of the Prior Art.

Some prior art drills utilize cavitational drilling techniques. Cavitation is a phenomenon whereby under certain conditions cavities form and violently collapse within a liquid. A shock wave results from the cavitation and may cause considerable mechanical damage to neighboring solid surfaces. Cavitation is induced in a drilling liquid by any suitable technique such as by the generation of acoustic energy. The cavitation threshold is a function of the physical properties of the liquid. The shock wave pressure is a function of the cavitation threshold. Hence, the shock wave pressure is not easily controlled or varied. Liquids having differing physical properties are necessary for creating different shock wave pressures. Since the shock wave pressure necessary to cause spalling of rock varies with the physical properties of the rock, the cavitation method may require different liquids for different rock in order to effect spalling. Also, the range of shock wave pressures achievable by cavitation is limited by the physical properties of the liquid. Thus, certain types of rock are incapable of being spalled by cavitation.

Currently most rock drilling is done by rotary drag bits or percussion bits. In both of these methods a bit made of hardened steel or other hard material scrapes or impacts against the rock until the rock material is disintegrated into a powder. The efficiency of such drills is very low. The rate of drilling and the cost increases greatly for hard formations and deep holes. In addition, the power lost in transmitting power to the rock reaches significant proportions.

The explosive drill, which is currently an operational alternative to rotary-percussion methods, is greatly restricted in application due to the high cost of explosive pellets.

SUMMARY OF THE INVENTION The general purpose of this invention is to provide a stress wave drill for drilling rock whose shock wave pressure is easily controlled and varied, that does not require different liquids for different rock, whose shock wave pressure is not limited in range, that is highly efficient, and that is more economical to operate than prior art drills. To achieve these significant advantages, one embodiment of the present invention provides an open-ended, hardened, drilling head containing an electrohydraulic pulser. The electrohydraulic pulser creates high-intensity stress waves capable of spalling the rock. These high-intensity stress waves are transmitted to the surface of the rock by a liquid which also serves as a carrier to remove spalled rock from the borehole.

Accordingly, one object of the present invention is to provide an easily controllable stress wave capable of spalling rock.

Another object of the present invention is to provide as easily variable stress wave capable of spalling rock.

Another object of the present invention is to provide a wide range of stress waves capable of spalling rock.

Another object of the present invention is to provide a highly efficient drill.

Another object of the present invention is to provide a highly economical drill.

Another object of the present invention is to provide a faster drilling rate.

Another object of the present invention is to provide drilling rates that are relatively independent of rock properties.

Another object of the present invention is to increase the percentage of total power of a drill that is transmitted to the rock.

Other objects and more complete appreciation of the present invention and its many attendant advantages will develop as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of a specific embodiment of the present invention.

FIG. 2 is a front elevation of the specific embodiment of FIG. 1.

FIG. 3 is a top view of a specific embodiment of the present invention.

FIG. 4 is a front elevation of the specific embodiment of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning to FIGS. 1 and 2, numeral I0 designates a drill stem. Attached to one end of drill stem I0 is an open-ended, hardened, drilling head 12. Hardened drilling head 12 is flared slightly to prevent jamming of drill stem 10 in the borehole I4. Hardened drill head 12 must be capable of withstanding the stress waves generated by electrohydraulic pulser 16 without cracking or breaking.

Electrohydraulic pulser 16 comprises a solid block of electrical insulating material 18. A high voltage electrode 20 extends through insulating material 18 and projects into the space inside drilling head 12. Two ground electrodes 22, located adjacent to high voltage electrode 20, also extend through insulating material 18 and project into the space inside drilling head 12. Solid block 18 prevents short circuiting of the discharge between electrodes 20 and 22. Electrodes 20 and 22 are enclosed in electrical insulation 24 inside drill stem 10. The description and operation of electrohydraulic pulser I6 is promulgated in detail in Browne, Allen and Schrom, Electrohydraulics, Science Journal, March 1968. Electrode support material 26 supports and protects the electrodes 20 and 22 from impact with spalled rock being carried out of the borehole I4 by fluid 28. Gasket 30 enables electrohydraulic pulser 16 to rotate within drill stem I0 and drilling head 12. Gasket 30 forms a fluid-tight seal between electrohydraulic pulser l6 and drill stem 10 and drilling head 12.

Referring to FIGS. 3 and 4, fluid 28 enters drill stem I0 via inlet port 34 and leaves drill stem 10 via outlet port 36. The direction of flow of fluid 28 is indicated by arrows 32. Fluid 28 serves as a carrier for spalled rock. Loose rock spalled by electrohydraulic pulser I6 is carried from the bottom of borehole 14 to outlet port 36, located near the top end of drill stem 10. Thus, the inside diameter of outlet port 36 must be large enough to pass the largest piece of spalled rock that will be produced by electrohydraulic pulser 16. The fluid 28 may be recycled through the drill provided the spalled rock is first removed therefrom. Electrohydraulic pulser 16 in conjunction with gasket 30 divides drill stem in two compartments 38 and 40. Of course. a plurality of compartments of various shapes are possible. The only requirement being that the compartments do not interrupt the fluid flow.

Shock waves from electrohydraulic pulser 16 travel through fluid 28 to the rock face 42. These stress waves load the face 42 which spalls on rebound. Rock particles spalled from the face 42 are removed by fluid 28 circulating through drill stem 10 and drilling head 12. The high-intensity stress waves generated by electrohydraulic pulser 16 are typically of microsecond duration. It is noted that electrohydraulic pulser 16 is but one means for generating high-intensity stress waves.

Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.

We claim:

1. A method of drilling a bore hole in a rock comprising the steps of:

a. moving a bifurcated drill stem downwardly into the bore hole at a controlled rate of movement;

b. generating adjacent the bottom of said bore hole stress waves, said stress waves being created by placing a set of three electrodes in said drill stem adjacent to said rock and energizing said electrodes with electrical energy;

c. controlling the magnitude and duration of the generated stress waves such that said stess waves spall the rock at the bottom of said bore hole in the vicinity of said electrodes; and

d. circulating a flow of drilling liquid downward through one section of said bifurcated drill stem and upwards through the the other section of said bifurcated drill stem. 

1. A method of drilling a bore hole in a rock comprising the steps of: a. moving a bifurcated drill stem downwardly into the bore hole at a controlled rate of movement; b. generating adjacent the bottom of said bore hole stress waves, said stress waves being created by placing a set of three electrodes in said drill stem adjacent to said rock and energizing said electrodes with electrical energy; c. controlling the magnitude and duration of the generated stress waves such that said stess waves spall the rock at the bottom of said bore hole in the vicinity of said electrodes; and d. circulating a flow of drilling liquid downward through one section of said bifurcated drill stem and upwards through the the other section of said bifurcated drill stem. 